A Staten Island high school football coach recalled in chilling detail Wednesday how he tried to save 15-year-old Nicholas Dellaventura as he lay dying on the playing field.

St. Joseph by-the-Sea coach Sean Cusick had just taken some freshman players off the field after practice into a workout room when he suddenly heard sirens blaring.

“I immediately ran outside and I see Nicholas laying on his back surrounded by all of his team members and one of their mother’s who happens to be a nurse.

“So I’m really nervous and shaken up and I ran over as fast as I could to help. She says, ‘I’’m certified in CPR. So I dropped to my knees and prepared to do CPR on Nicholas, “ said Cusick.

But he stopped because he could see Nicholas was still breathing.

“That is when I realized that he was coherent and his breathing was very labored. He couldn’t speak, but he was coherent. He was trying very hard to breath. His chest was rising up and down very quickly.”

We all called for medics and the [ambulance] arrived in two minutes flat “ he said.

”There was no way that work out could have done that to him. He was running basic drills.”

Earlier, his heartbroken aunt told The Post.the that her nephew had no pre-existing medical conditions,

He “was healthy and strong. That’s why this is such a shock. There isn’t a history of serious heart problems in the family. This was completely out of the blue,” Jane Bernstein, 51, said on Wednesday.

Autopsy results are still pending.

“Nicky was really such an exceptional person, especially for his age. He was the sweetest, gentlest, kindest kid you could ever know. His siblings are the same way. Nicky was a big guy, he was huge, but he was just such a teddy bear inside. Everyone loved him. This is just horrible. This family has a strong faith in God and we’re just praying for Nicky right now.

She added: “If you look at his Facebook page, so many kids are posting really sweet messages. And there is the same theme throughout all the posts. They say, Nicky you were the nicest kid I ever knew or Nicky you were like a big brother to me, we’re all going to miss you so much. So that is all so surreal, we cant believe this. Just the other day he was here laughing and smiling and the next he’s gone.”

“He loved playing video games and absolutely adored football. He lived and breathed it. He would always watch the Jets, his favorite team, on TV. He was a very good student and he excelled in Math. He was a really smart kid,” Bernstein said.

“Nicky was full of love. One day, he would have made a great husband and a great dad. We could see it in him. He was so much like his dad, a really great guy. He had so much potential. We love him so so much.

“We don’t know why this happened. The answer is out there somewhere.”

Greg Manos, 45, athletic director of St. Joseph’s by-the-Sea HS and head football coach from 2002-2010, said the school followed state mandated protocol.

“We have things in place that deal with the temperature. The kids aren’t out there in full gear. They are in shorts and t-shirts. There no heavy gear. We wait until 5 [p.m.] at night to start the practices when its cooler.”